1. Field of the Invention
The present invention relates to a liquid crystal display (LCD) device, and more particularly, to an LCD device and a method for manufacturing the same in which if an overcoating layer is not formed on a color filter substrate, a gap between exposed pigments is filled with a column spacer material to increase a process margin.
2. Discussion of the Related Art
Demands for various display devices have increased with the development of an information based society. Accordingly, many efforts have been made to research and develop various flat display devices such as liquid crystal display (LCD), plasma display panel (PDP), electroluminescent display (ELD), and vacuum fluorescent display (VFD). Some species of flat display devices have already been applied to displays for various equipment.
Among the various flat display devices, liquid crystal display (LCD) devices have been most widely used due to advantageous characteristics of a thin profile, light weight, and low power consumption. The LCD devices provide a substitute for a Cathode Ray Tube (CRT). In addition to mobile type LCD devices such as a display for a notebook computer, LCD devices have been developed for computer monitors and televisions to receive and display broadcasting signals.
In order to use LCD devices in various fields as a general display, the key to developing LCD devices depends on whether LCD devices can implement a high quality picture, such as high resolution and high luminance with a large-sized screen, while still maintaining the characteristics such as lightness in weightness, thin profile, and low power consumption.
Hereinafter, a related art LCD device will be described with reference to the accompanying drawings.
FIG. 1 is an exploded perspective view illustrating a related art twisted nematic (TN) mode LCD device.
As shown in FIG. 1, the related art TN mode LCD device includes first and second substrates 1 and 2 bonded to each other with a certain space therebetween, and a liquid crystal layer 3 formed by injection, between the first and second substrates 1 and 2. The first and second substrates 1 and 2 and the liquid crystal layer 3 are referred to as a liquid crystal panel.
In more detail, the first substrate 1 includes a plurality of gate lines 4 arranged along a first direction at fixed intervals and a plurality of data lines 5 arranged along a second direction perpendicular to the first direction at fixed intervals. A plurality of pixel regions P are defined by the gate and data lines 4 and 5. A plurality of electrodes 6 are arranged within the pixel regions P. A plurality of thin film transistors T are formed at regions where the gate lines cross the data lines and apply data signals of the data lines 5 to the pixel electrodes in accordance with signals supplied to the gate lines.
The second substrate 2 includes a black matrix layer 7 that prevents light from portions except the pixel regions P, R/G/B color filter layers 8 formed to correspond to the pixel regions, for displaying various colors, and a common electrode 9 for producing the image on the color filter layers 8.
In the aforementioned LCD device, the liquid crystal layer 3 is formed between the first and second substrates 1 and 2, wherein liquid crystal molecules of the liquid crystal layer 3 are driven by an electric field generated between the pixel electrode 6 and the common electrode 9. That is, an alignment direction of the liquid crystal molecules of the liquid crystal layer 3 is controlled by an induced electric field thereto. Accordingly, light irradiated through the liquid crystal layer 3 may be controlled by the alignment direction of the liquid crystal molecules, thereby displaying the image.
This kind of LCD device is referred to as a TN mode LCD device. The TN mode LCD has disadvantageous characteristics such as a narrow viewing angle. In order to overcome this problem of the narrow viewing angle, an in-plane switching (IPS) mode LCD device has been actively developed.
Hereinafter, a related art IPS mode LCD device provided with column spacers will be described with reference to the accompanying drawings.
FIG. 2 is a plan view illustrating the related art IPS mode LCD device, and FIG. 3 is a structural sectional view taken along line I˜I′ of FIG. 2.
As shown in FIG. 2 and FIG. 3, the related art IPS mode LCD device includes first and second substrates 30 and 40 bonded to each other with a certain space, and a liquid crystal layer 55 formed between the first and second substrates 30 and 40 by injection. The first and second substrates 30 and 40 and the liquid crystal layer 55 are referred to as a liquid crystal panel.
The Related Art IPS mode LCD device has the same structure as that of the aforementioned related art TN mode LCD device of FIG. 1 except that the common electrode of the second substrate in the TN mode LCD device is replaced with an overcoating layer.
In more detail, the first substrate 30 includes a plurality of gate lines 31 arranged along a first direction at fixed intervals and a plurality of data lines 32 arranged along a second direction perpendicular to the first direction at fixed intervals. A plurality of pixel regions P are defined by the gate and data lines 31 and 32. A plurality of thin film transistors (TFT) are formed at regions where the gate lines cross the data lines. Pixel electrodes 33 and common electrodes 35a are alternately formed in the pixel regions.
The common electrodes 35a are formed in parallel with the data lines 32 and forked from common lines 35 formed to be flush with the gate lines 32.
Each of the thin film transistors includes a gate electrode 31a extended from the gate line 31, a semiconductor layer 34 formed to cover the gate electrode 31a, a source electrode 32a extended from the data line 32 to correspond to both sides of the semiconductor layer 34, and a drain electrode 32b spaced apart from the source electrode 32a at a predetermined interval.
A gate insulating film 36 is formed on an entire surface of the first substrate 30 including the gate lines 31 and the data lines 32 to insulate respective metal lines from each other. A passivation film 37 is formed on the gate insulating film 36 including the data lines 32.
Also, the second substrate 40 facing the first substrate 30 includes a black matrix layer 41 that prevents light from portions (portions for gate and data lines and thin film transistors) except the pixel regions, R/G/B color filter layers 42 formed to correspond to the pixel regions, and an overcoating layer 43 for planarizing an entire surface of the second substrate 40 including the color filter layers 42. A plurality of column spacers 50 are formed on a predetermined portion of the overcoating layer 43 to maintain a cell gap between the first and second substrates 30 and 40.
The respective column spacers 50 are spaced apart from each other at constant intervals to correspond to the gate lines 31. The column spacers 50 support the first and second substrates 30 and 40 to maintain the cell gap.
Meanwhile, the related art LCD devices have been manufactured by a liquid crystal injection method.
The liquid crystal injection method will now be described in brief.
First, an LCD panel and a container having liquid crystal material therein are provided in a chamber, wherein the chamber is maintained in a vacuum state. That is, moisture and air bubbles of the liquid crystal material and the container are removed simultaneously, and an inside space of the LCD panel is maintained in a vacuum state. Then, a liquid crystal injection inlet of the LCD panel is dipped into the container having the liquid crystal material in the vacuum state, and the vacuum state inside the chamber is changed to an atmospheric pressure. Thus, the liquid crystal material is injected to the inside of the LCD panel through the liquid crystal injection inlet according to a pressure difference between the inside of the LCD panel and the chamber.
However, the LCD device manufactured by the liquid crystal injection method has the following disadvantages.
First, after cutting the substrate into the respective LCD panel regions, the liquid crystal injection inlet is dipped into the container having the liquid crystal material while maintaining the vacuum state between the two substrates. Thus, it takes a great amount of time to inject the liquid crystal material between the two substrates, thereby lowering yield.
Second, in case of forming a large sized LCD device, it is difficult to completely inject the liquid crystal material into the inside of the LCD panel, thereby causing the failure due to incomplete injection of the liquid crystal material.
Third, it takes a great amount of time to inject the liquid crystal material, and it requires a large space for liquid crystal injection devices.
Fourth, in a case of using ball spacers, a defect occurs in which individual ball spacers are conglomerated with each other to twinkle. Alternatively, since the ball spacers are dispersed within pixels, light leakage occurs.
The above problems of the liquid crystal injection method have become serious due to the trend manufacturing large sized LCD panels. In order to overcome the problems of the liquid crystal injection method, a liquid crystal dispersion method has been developed. In the dispersion method, two substrates are bonded to each other after dispersing liquid crystal material on either one of the two substrates.
In the related art IPS mode LCD device, the overcoating layer formed on the color filter substrate to planarize the substrate is thick and its material cost is high. Therefore, efforts to remove the overcoating layer have been suggested.